{"id":75038,"date":"2017-01-14T00:00:00","date_gmt":"2017-01-14T00:00:00","guid":{"rendered":"https:\/\/www.fertilitysmarts.com\/2017\/01\/14\/an-intro-to-preimplantation-genetic-testing-pgt"},"modified":"2023-11-09T22:29:21","modified_gmt":"2023-11-09T22:29:21","slug":"an-intro-to-preimplantation-genetic-testing-pgt","status":"publish","type":"post","link":"https:\/\/www.fertilitysmarts.com\/intro-to-preimplantation-genetic-testing-pgs\/2\/1205","title":{"rendered":"An Intro to Preimplantation Genetic Testing (PGT)"},"content":{"rendered":"
If you’re planning to undergo in vitro fertilization (IVF)<\/a>, you may have heard the term preimplantation genetic testing (PGT). It’s an option available to individuals or couples undergoing IVF, and it involves genetically screening the embryos before embryo transfer.<\/p>\n There are multiple types of PGT testing:<\/p>\n These tests can be done:<\/p>\n If you’re curious about or are considering PGT, it can help understand how this testing is carried out and whether you are likely to benefit. Here we’ll take a look at PGT in-depth, starting with PGT-A.<\/p>\n To understand PGT-A genetic testing of embryos for aneuploidy, you must first grasp some basic cell biology. Each cell in the body has 46 chromosomes, except eggs and sperm, which each have 23. The egg and sperm combine to give the offspring a total of 46 chromosomes. We inherit half of our chromosomes from our biological father and the other half from our biological mother. These chromosomes act like instruction books and control the function of our cells.<\/p>\n If an egg or a sperm is missing a chromosome, then the embryo created from that egg or sperm will also be missing a chromosome and a whole set of instructions. If there is an extra chromosome in an egg or sperm, the embryo will be abnormal, having twice as many copies of those instructions then it should have. Down Syndrome is one example of a genetic disorder caused by an additional copy of a chromosome.<\/p>\n <\/p>\n Most such embryos will not implant at all, some will cause an early miscarriage, and some can go to full term and be born. Almost all of the babies born with extra or missing chromosomes will have some kind of physical and\/or mental disability.<\/p>\n In most studies, preimplantation genetic testing has not been shown<\/a> to improve pregnancy rates for the general population undergoing IVF. However, it has been shown to:<\/p>\n If you are considering testing your embryos during an IVF cycle, you might be referred to a genetic counselor who will ask extensive questions about your family history. This counselor will also consider the age of the female partner and tell you your chances of having normal embryos during your IVF cycle. Many genetic laboratories will also review the fees and accuracy of the testing ordered by your doctor.<\/p>\n A genetic counselor and your doctor should discuss the pros and cons of testing your embryos as per your specific situation and whether it\u2019s the right decision for you.<\/p>\n It\u2019s possible to test each embryo created by IVF and count the number of chromosomes.<\/p>\n This is done by:<\/p>\n If embryos are tested on day five or day six at the blastocyst stage, they usually have to be frozen because the results aren\u2019t available in time for a fresh transfer. A few clinics offer overnight testing, and this option may become more available with time and better technology.<\/p>\n Some clinics offer to test the \u201cspare\u201d embryos from an IVF cycle. In this case, you get a fresh transfer of untested embryos, and any extra embryos of suitable quality will be biopsied before being frozen.<\/p>\n The removal of cells from the embryo at these early stages does not affect the embryo or fetal development. The embryo can usually compensate for the damage within a few cell divisions. In good hands, the biopsy of an embryo has little effect on its growth, although it may slow down slightly.<\/p>\n That said, the biopsy itself is invasive, and there is a chance that a normal embryo that would have otherwise implanted could be damaged beyond repair. This is a major risk in PGT: it can compromise the viability of the embryo tested. Note that this will not lead to abnormalities in a baby. In this case, the embryo has been damaged so that it is no longer able to implant.<\/p>\n If no embryos develop to the blastocyst stage of development, no testing can or will be performed.<\/p>\n\n
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What are chromosomes, and why do they matter for PGT-A?<\/h2>\n
Why undergo preimplantation genetic testing for aneuploidy (PGT-A)?<\/h2>\n
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Genetic Counseling as Part of the PGT Process<\/h2>\n
How Embryos Are Tested During PGT<\/h2>\n
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PGT and Embryo Growth<\/h2>\n